The general morphology of small, isometric, RNA-containing viruses has been delineated in a number of studies but considerably less is known concerning the structure and interactions at the molecular level. The object of this proposal is to determine specific features of the structures of RNA and protein components of R17 phage and of turnip- yellow- mosaic virus. The intramolecular and intermolecular interactions which stabilize the viral structure will also be studied. Raman and infrared spectroscopy will be used to determine (1) the percent of RNA bases in single-stranded and double-stranded regions.(2) the percent of bases in hydrogen-bonded ( percent AU pairs and percent GC pairs) and in base-stacked configurations, (3) the amount of order in the ribose-phosphate linkages of the RNA backbone, (4) the amount of alpha- helical and beta-type structures in the protein subunits of the capsid and (5) the presence of aromatic side-chain residues and disulfide linkages in the protein subunit. Melting-point curves and treatment with reagents which break hydrogen bonds (e.g. urea and formamide) will give information on the relative stabilities of the RNA- RNA, RNA-protein and protein-protein interactions. The results will be interpreted in terms of the assembly and disassembly of the viruses.